1. Field of the Invention
The invention generally relates to the area of digital communication. Specifically the invention relates to a system capable of receiving satellite transmissions.
2. Related Art
The utilization of digital communication systems is growing at a rapid pace in modern society. Specifically, digital communication systems have become more common because they typically provide a higher level of performance than analog communication systems. As a result, communication systems such as television and radio are transitioning from analog systems to digital systems. Radio is transitioning from analog AM, FM and SW transmissions to digital and satellite radio transmissions. Similarly, television systems are transitioning to digital systems such as digital cable, digital television (“DTV”), high-definition television (“HDTV”), and satellite. In the case of television, satellite video transmissions are common and widespread around the world. Additionally, from the inception of convenient direct broadcast satellite (“DBS”) services such as those provided by DBS service providers DIRECTV® and DISH Network® in the United States and similar services around the world, there has been a tremendous growth in the number of DBS subscribers.
Unfortunately, known satellite equipment utilized for receiving satellite video transmissions are not as user friendly as the old terrestrial analog television equipment. Specifically, known satellite equipment typically lacks the ability to allow a user to utilize two or more reception channels simultaneously.
An example of this problem is shown in FIG. 1. In FIG. 1, a typically known DBS satellite reception system 100 having a DBS satellite antenna 102 (such as a parabolic reflector antenna known generally as a “dish antenna” or “dish”), a low-noise block converter (“LNB,” also known as a low-noise block downconverter) 104 and a set-top converter box (generally known as set-top box “STB” and/or Integrated Receiver Decoder “IRD”) 106 is shown. The LNB 104 is in signal communication with the DBS satellite antenna 102 and STB 106 via signal paths 108 and 110, respectively. The STB 106 may be typically a satellite receiver with a built-in decoder for unscrambling subscription channels broadcast by the DBS system provider (not shown). The STB 106 may be any generally known STB similar to the STBs produced by multiple manufacturers for both DIRECTV® and DISH Network®, or other similar types of DBS service providers.
In the case of a parabolic reflector antenna, it is appreciated by those skilled in the art that the DBS satellite antenna 102 and LNB 104 are packaged usually together as one unit and the LNB 104 is typically an active device. Examples of the DBS satellite antenna 102 may include an 18-inch parabolic reflector antenna or any other type of antenna such as a phased array, resonant plane, microstrip, patch, and/or active or passive antenna.
The LNB 104 is generally an amplifier that blocks low-end frequencies and receives the high-end frequencies utilized in DBS satellite transmissions. In many DBS systems utilizing a parabolic reflector antenna, the LNB 104 is generally located at the horn feed at the end of the arm projecting from the DBS satellite antenna 102. Typically, a single-output LNB provides one RF output for connecting a coaxial cable to feed a received DBS satellite signal to a single STB. A dual-output LNB typically has two RF outputs for distributing DBS satellite signals to two or more STBs. In a DBS satellite reception system 100, the LNB 104 typically downconverts received DBS satellite signals from a Ku-band signal (such as in the 12.2 GHz to 12.7 GHz range) to an L-band signal (such as 950 MHz to 2150 MHz range).
In an example of operation of the DBS satellite reception system 100, the DBS satellite antenna 102 receives DBS satellite signals 112 from a DBS satellite 114 and passes them to the STB 106, via signal path 110, after downconvertering the DBS satellite signals 112 with the LNB 104 (or LNBs if more than one). The STB 106 then tunes to and decodes a desired frequency channel of media content and passes that media content to an end media device (not shown) such as television, radio, video monitor, recording device or broadband modem where the media content may be video, audio and/or data.
Until recently, most DBS systems such as DBS satellite reception system 100 have not allowed multiple STBs (such as STB 106) to operate in combination with one or more DBS satellite antennas (such as DBS satellite antenna 102) because usually a STB (such as STB 106) has some type of intelligence (i.e., it has a processor, microprocessor, controller and/or microcontroller that runs some type of control software for the STB) that controls the LNB 104 (or LNBs) based on the desired frequency channels of media content that the STB 106 desires.
Additionally in the usual operation a DBS satellite system, such as DIRECTV® and DISH Network®, the DBS satellite system typically broadcasts each channel from their satellites with either a “left-hand” (known as left-handed circular polarization or “LHCP”) or “right-hand” (known as right-handed circular polarization or “RHCP”) circular polarization. Approximately half the frequency channels are broadcast with one polarization while the other frequency channels are broadcast with the opposite polarization.
Generally, the LNB 104 is capable of only receiving one type of polarization at a time and the STB 106 has an internal memory (not shown) that typically contains a table of values (that is typically downloaded from the DBS satellite 114) that represent the polarization of each frequency channel. The STB 106 then instructs the LNB 104, via signal path 110 (which may be a standard coaxial cable), to switch to the polarization that corresponds to the desired frequency channel of the STB 106. The STB 106 usually instructs the LNB 104 to switch between polarizations by placing a variable voltage on the signal path 110.
As a result, the DBS satellite reception system 100 does not allow multiple STBs to operate on one coaxial cable from the DBS satellite antenna 102 and LNB 104 combination because multiple STBs would not be able to coordinate switching the polarization of the LNB 104. The polarization of a frequency channel selection of one STB would interfere with the polarization of another channel selection on the other STB.
In a typical home environment this is a drawback for DBS systems compared to, as an example, standard non-DBS analog cable systems (i.e., cable television) and old terrestrial analog television equipment (i.e., standard over-the-air television and radio transmissions generally known as “terrestrial transmission systems”). In cable systems, a cable provider transmits the cable channels (whether analog, digital or combination of both) via one coaxial or fiber optic cable to a home. Additionally, in a terrestrial transmission system a user may utilize an external television antenna (generally known as the “outside antenna”) to receive the terrestrial transmissions and feed them into the home via a single coaxial cable.
The end-users, such as residents of the home, may then split the coaxial cable with a general-purpose splitter into multiple coaxial cables that are capable of feeding the transmitted cable channels into multiple video monitors or recording devices via multiple cable receivers (or built-in television receivers within the video monitors and most recording devices such as video recorders and digital recorders). Each cable receiver is then capable of independently and simultaneously selecting different received cable or terrestrial frequency channels.
At present, the end-users in a home environment have become accustomed to connecting multiple video monitors, recording devices and/or cable receivers to a common coaxial system that is the result of simply splitting the input coaxial cable from the cable system. It is appreciated that in a typical modern home almost every room will have a coaxial cable that extends from a wall outlet. All these cables will be connected to either the outside antenna or the cable system via the coaxial splitter. As a result, the end-users in, a home environment expect, or at least desire, a similar convenience from an installed DBS satellite system. Unfortunately, the DBS satellite reception system 100 is not capable of allowing multiple STBs to connect to the LNB 104 and provide independent simultaneous channel reception by each individual STB.
Present attempts to solve this problem include utilizing multiple LNBs for each STB along with potentially utilizing multi-switches. However, these solutions are multi-cable approaches that are high cost and cumbersome to arrange in the typical home environment because they entail the increased cost of equipment such as multiple cables, multi-switch devices, combiners and splitters and the cost of labor in professionally installing the equipment. Once the equipment has been installed it is pseudo-permanent in nature because it is difficult to rearrange the equipment in the future. These approaches are still much more complicated than adding additional cable-ready tuners in a home-installed cable television system.
Therefore, there is a need for a system and method that provides a low cost solution for distributing DBS satellite signals on a single cable from the DBS satellite antenna to the home environment.
If multiple DBS satellite signals are distributed on a single cable from the DBS satellite antenna 102, FIG. 1, to the home environment, the resulting example of the frequency spectrum may be described as a plot 200 of the magnitude 202 versus frequency 204 of the frequency spectrum of the multiple DBS frequency channels on a DBS satellite transmission as shown in FIG. 2. In FIG. 2, the frequency channels, such as frequency channel 1 centered at carrier center frequency Fc1 206, frequency channel 2 centered at carrier center frequency Fc2 208, and frequency channel N centered at carrier center frequency FcN 210, are continuously distributed in plot 200 of the frequency spectrum.
The typical STB 106 is not capable of receiving all the frequency channels shown in plot 200. Therefore, allowing an end-user to view one frequency channel on a video monitor while simultaneously recording another frequency channel on a video recorder and/or watching one of more frequency channels within the typical picture-in-picture functions of most modern video monitors is not possible because generally known state-of-the-art DBS satellite STBs (such as STB 106) typically utilize, as an example, a STB architecture 300 shown in FIG. 3, where the STB architecture 300 is only capable of demodulating and decoding one frequency channel at a time.
In FIG. 3, the STB architecture 300 may include frequency converter 302 (such as a mixer), a frequency source 304, a filter 306, an analog-to-digital converter (“ADC” or “A/D”) 308, and a digital signal processing (“DSP”) unit 310. In typical operation, a received LNB downconverted DBS satellite signal 312, from the LNB 104, is frequency converted (i.e., mixed) with the output of the frequency source (such as a local oscillator) 304, where the frequency source 304 generates a carrier frequency (“Fc”) at the frequency converter 302.
The frequency converter output 314 is then passed to the filter 306, where the filter 306 is a band-pass filter if the frequency converter output 314 is a low intermediate frequency (“IF”) signal or it is a low-pass filter if the frequency converter output 314 is a baseband signal. The resulting filter output signal 316 is then passed to the ADC 308, which converts the filter output signal 316 to a digital signal 318 that is passed to the DSP unit 310 for demodulating and/or decoding the media content on the digital signal 318. The resulting processed signal 320 is then passed to a media device (not shown) such as a television, DTV, HDTV, recording device such as a video cassette recorder (“VCR”), digital video recorder (“DVR”), recordable digital video disk (“DVD”), radio, home theater system, computer and/or broadband modem. Unfortunately, the STB architecture 300 is unable to demodulate multiple DBS satellite frequency channels simultaneously because it describes a single tuner-demodulator architecture.
An example attempt to solve this problem is shown in FIG. 4 that may utilize multiple channel tuner-demodulator 400 that includes multiple demodulator branches that are similar to the demodulator shown in FIG. 3. In FIG. 4, the first branch of the implementation of the demodulator similar to FIG. 3 402 tunes the frequency source (that may include a local oscillator) 404 to carrier center frequency Fc1 for channel 1. A similar process is performed for Channel 2 406 up to Channel N 408. Similar to FIG. 3, branch 402 may include a frequency converter 410, the frequency source 404, a filter 412, an ADC 414, and a DSP unit 416. Similarly, branch 406 may include a frequency source 418, a frequency source 420, a filter 422, an ADC 424, and a DSP unit 426, and branch 408 may include a frequency converter 428, a frequency source 430, a filter 432, an ADC 434, and a DSP unit 436. The branches 402, 406 and 408 process the received digital signal 438 and produce branch outputs 440, 442 and 444, respectively.
Unfortunately, the multiple channel tuner-demodulator 400 is too complex and expensive for consumer applications. Therefore, there is a need for a cost-efficient system and method for simultaneously demodulating multiple channels that are contiguous in the frequency domain.